1. Field of the Invention
The present invention relates to a thermosensitive recording material, and more particularly to an improved thermosensitive recording material having good preservability such as the light resistance of the recorded image and the background, and a high degree of background whiteness, and a production process thereof.
2. Discussion of the Background
Presently, a thermosensitive recording material, is known in which a thermosensitive coloring layer is provided on a substrate, such as a sheet of paper, synthetic paper, or plastic film. The thermosensitive coloring layer includes a colorless or pale-colored coloring agent, such as a leuco dye, a coloring developer for inducing color formation in the leuco dye upon application of heat thereto, such as a phenolic compound and organic acid, a binder, and, if necessary, a filler, a thermosensitizer, a lubricant, and auxiliary agents, which are mixed, dispersed, coated on a substrate, and dried to form a thermosensitive coloring layer. Such a thermosensitive recording material and production process have been disclosed in, for example, JP-P 43-4160, JP-P 45-14039 and JP-P 48-27736, and have been used for various purposes.
Since the thermosensitive recording image can be rapidly recorded by the chemical reaction of a coloring agent with a coloring developer, the thermosensitive recording process has the following advantages:
(1) images can be rapidly recorded by a relatively simple apparatus without complicated, steps, such as development and fixing; PA1 (2) images can be recorded without producing noise and environmental pollution; PA1 (3) various colored images, for example, red, blue, violet, and black, can be easily obtained; and PA1 (4) the manufacturing cost is low. PA1 3,3-bis(p-dimethylaminophenyl)phthalide, PA1 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophtalide (or Crystal Violet Lactone), PA1 3,3-bis(p-dimethylaminophenyl)-6-diethylaminophtalide, PA1 3,3-bis(p-dimethylaminophenyl)-6-chlorophtalide, PA1 3,3-bis(p-dibutylaminophenyl)phtalide, PA1 3-cyclohexylamino-6-chlorofluoran, PA1 3-dimethylamino-5,7-dimethylfluoran, PA1 3-diethylamino-7-chlorofluoran, PA1 3-diethylamino-7-methylfluoran, PA1 3-diethylamino-7,8-benzfluoran, PA1 3-diethylamino-6-methyl-7-chlorofluoran, PA1 3-(N-p-tolyl-N-ethylamino)-5-methyl-7-anilinofluoran, PA1 3-pyrrolidino-6-methyl-7-anilinofluoran, PA1 2-[N-(3'-trifluoromethylphenyl)amino]-6-diethylaminofluoran, PA1 2-[3,6-bis(diethylamino)-9-(o-chloroanilino)xanthyl]-benzoic acid lactam, PA1 3-diethylamino-6-methyl-7-(m-trichloromethylanilino)fluoran, PA1 3-diethylamino-7-(o-chloroanilino) fluoran, PA1 3-di-n-butylamino-7-(o-chloroanilino) fluoran, PA1 3-(N-methyl-N-n-amylamino)-6-methyl-7-anilinofluoran, PA1 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, PA1 3-diethylamino-6-methyl-7-anilinofluoran, PA1 3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran, PA1 benzoyl leuco methylene blue, PA1 6'-chloro-8'-methoxy-benzoindolino-spiropyran, PA1 6'-bromo-3'-methoxy-benzoindolino-spiropyran, PA1 3-(2'-hydroxy-4'-dimethylaminophenyl)-3(2'-methoxy-5'-chlorophenyl)phthalid e, PA1 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-nitrophenyl)phtalide PA1 3-(2'-hydroxy-4'-diethylaminophenyl)-3(2'-methoxy-5'-methylphenyl)phtalide, PA1 3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-methylphen yl)phtalide, PA1 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, PA1 3-(N-ethyl-N-2-ethoxypropylamino)-6-methyl-7-anilinofluoran, PA1 3-N-methyl-N-isobutyl-6-methyl-7-anilinofluoran, PA1 3-morphorino-7-(N-propyl-trifluoromethylanilino)fluoran, PA1 3-pyrrolidino-7-m-trifluoromethylanilinofluoran, PA1 3-diethylamino-5-chloro-7-(N-benzyl-trifluoromethylanilino)fluoran, PA1 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluoran, PA1 3-diethylamino-5-chloro-7-(.alpha.-phenylethylamino) fluoran, PA1 3-(N-ethyl-p-toluidino) -7-(.alpha.-phenylethylamino) fluoran, PA1 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, PA1 3-diethylamino-5-methyl-7- (.alpha.-phenylethylamino) fluoran, PA1 3-diethylamino-7-piperidinofluoran, PA1 2-chloro-3-(N-methyltoluidino)-7-(p-n-butylanilino)fluoran, PA1 3-(N-methyl-N-isopropylamino)-6-methyl-7-anilinofluoran, PA1 3-di-n-butylamino-6-methyl-7-anilinofluoran, PA1 3,6-bis(dimethylamino)fluorenespiro(9,3')-6'-dimethylaminophtalide, PA1 3-(N-benzyl-N-CyClohexylamino)-5,6-benzo-7-.alpha.-naphtylamino-4'-bromoflu oran, PA1 3-diethylamino-6-chloro-7-anilinofluoran, PA1 3-diethylamino-6-methyl-7-mesidino-4', 5'-benzofluoran, PA1 3-N-methyl-N-isopropyl-6-methyl-7-anilinofluoran, PA1 3-N-ethyl-N-isoamyl-6-methyl-7-anilinofluoran, and PA1 3-diethylamino-6-methyl-7-(2', 4'-dimethylanilino)fluoran. PA1 4,4'-isopropylidenediphenol, PA1 4,4,'-isopropylidenebis(o-methylphenol), PA1 4,4,'-sec-butylidenebisphenol, PA1 4,4,'-isopropylidenebis(2-tert-butylphenol), PA1 zinc p-nitrobenzoate, PA1 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, PA1 2,2-(3,4,'-dihydroxydiphenyl)propane, PA1 bis(4-hydroxy-3-methylphenyl)sulfide, PA1 4-[.beta.-(p-methoxyphenoxy)ethoxy]salicylate, PA1 1,7,bis(4-hydroxyphenylthio)-3,5-dioxaheptane, PA1 1,5-bis(4-hydroxyphenylthio)-5-oxapentane, PA1 monocalcium salts of monobenzylphtalate, PA1 4,4,'-cyclohexylidenediphenol, PA1 4,4,'-isopropylidenebis(2-chlorophenol), PA1 2,2,'-methylenebis(4-methyl-6-tert-butylphenol), PA1 4,4,'-butylidenebis(6-tert-butyl-2-methylphenol), PA1 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, PA1 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, PA1 4,4,'-thiobis(6-tert-butyl-2-methylphenol), PA1 4,4'-diphenolsulfone, PA1 4-isoproxy-4'-hydroxydiphenylsulfone, PA1 4-benzyloxy-4'-hydroxydiphenylsulfone, PA1 4,4'-diphenolsulfoxide, PA1 isopropyl p-hydroxybenzoate, PA1 benzyl p-hydroxybenzoate, PA1 benzyl protocatechuate, PA1 stearyl gallate, PA1 lauryl gallate, PA1 octyl gallate, PA1 1,3-bis(4-hydroxyphenylthio)propane, PA1 N,N'-diphenylthiourea, PA1 N,N'-di(m-chlorophenyl)thiourea, PA1 salicylanilide, PA1 bis(4-hydroxyphenyl)methyl acetate, PA1 bis (4-hydroxyphenyl)benzyl acetate, PA1 1,3-bis(4-hydroxycumyl)benzene, PA1 1,4-bis(4-hydroxycumyl)benzene, PA1 2,4'-diphenolsulfone, PA1 2,2,-diallyl-4,4'-diphenolsulfone, PA1 3,4-dihydroxyphenyl-4'-methyldiphenylsulfone, PA1 zinc 1-acetyloxy-2-naphthoate, PA1 zinc 2-acetyloxy-1-naphthoate, PA1 zinc 2-acetyloxy-3-naphthoate, PA1 .alpha.,.alpha.-bis (4-hydroxyphenyl)-.alpha.-methyltoluene, antipyrine complex of zinc thiocyanate, PA1 tetrabromobisphenol A, PA1 tetrabromobisphenol S, PA1 4,4,'-thiobis(2-methylphenol), PA1 4,4,'-thiobis(2-chlorophenol), PA1 o-(benzenesulfonylaminocarbonyl) benzoic acid methyl ester, PA1 o-(benzenesulfonylaminocarbonyl)benzoic acid ethyl ester, PA1 4,4'-bis(ptoluenesulfonylaminocarbonylamino)diphenylmethane, PA1 4,4,'-bis(p-toluenesulfonylaminocarbonylamino)diphenylsulfide, PA1 4,4,'-bis(p-toluenesulfonylaminocarbonylamino)diphenylether, PA1 3,4,'-bis(p-toluenesulfonylaminocarbonylamino)diphenylether, PA1 1,2-bis(4-(p-toluenesulfonylaminocarbonylamino)phenyl)ethane, and PA1 2,8-dimethyl-3,7-(p-toluenesulfonylaminocarbonylamino)dibenzothiophenyl-5,5 -dioxide. PA1 polyvinyl alcohol, PA1 carboxy-modified polyvinyl alcohol, PA1 starch and starch derivatives, PA1 cellulose derivatives such as methoxycellulose, PA1 hydroxyethylcellulose, carboxymethylcellulose, PA1 methylcellulose, and ethylcellulose, PA1 sodium salts of polyacrylic acid, PA1 polyvinylpyrrolidone, PA1 acrylamide-acrylate copolymer, PA1 acrylamide-acrylate-methacrylic acid copolymer, PA1 alkali salts of styrene-maleic anhydride copolymer, PA1 alkali salts of isobutylene-maleic anhydride copolymer, PA1 polyacrylamide, PA1 sodium alginate, PA1 gelatin, and PA1 casein, PA1 styrene-butadiene copolymer, PA1 styrene-butadiene-acrylate copolymer, PA1 polyvinyl acetate, PA1 vinyl acetate-acrylic acid copolymer, PA1 styrene-acrylate copolymer, PA1 polyurethane, PA1 polyacrylate, PA1 polymethacrylate, PA1 vinyl chloride-vinyl acetate copolymer, and PA1 ethylene-vinyl acetate copolymer.
Because of these advantages, this type of thermosensitive recording material is widely used for price labels in stores. The thermosensitive recording material has wide-scale utilization not only as a recording material for price labels in stores, but also for copying documents and for printers for electric computer (CAD), facsimile machines, telex, ticket vendors, label printers for various industrial uses, and medical measuring instruments and the like.
However, the thermosensitive recording material has the shortcoming the recorded image easily fades away and the background area tends to color when the recorded image and the background area are exposed to sunlight or the light of a fluorescent lamp. This is caused by a change in the chemical composition of the recorded image or the coloring agent.
In an attempt to solve these problems, several proposals have been made. For example, JP-A 54-18752 discloses a thermosensitive recording material in which a benzophenolic ultraviolet stabilizer or a phenolic antioxidant is contained in the thermosensitive coloring layer including a coloring agent and a phenolic substance for inducing color formation in the coloring agent. JP-A 60-112487 discloses a thermosensitive recording material including a thermosensitive coloring layer, and a protective layer which is formed on a thermosensitive coloring layer and is included an ultraviolet stabilizer. JP-A 61-134292 discloses a thermosensitive recording material in which a thermosensitive coloring layer includes a pigment or dye absorbing the light in the region of 400 to 600 nm. JP-A 61-193883 discloses a thermosensitive recording material in which a protective layer includes a benzotriazol type ultraviolet stabilizer.
One problem which occurs, however, is that thermosensitive materials using an ultraviolet stabilizer in a thermosensitive coloring layer or a protective layer appear yellow or pale-yellow because the ultraviolet stabilizer tends to absorb light near 400 nm. To address this problem, it has been proposed that a fluorescent brightening agent be included in the thermosensitive coloring layer or that a protective layer for whitening be used. JP-A 62-184880 discloses a thermosensitive recording material having a protective layer including a diamino stilbene disulfonic acid type fluorescent brightening agent.
Another problem which occurs is that the preservability, such as the light resistance of the thermosensitive recording material, deteriorates. This is attributed to the fact that the ultraviolet stabilizer loses its ability to absorb ultraviolet rays by reaction with a fluorescent brightening agent. Furthermore, a fluorescent brightening agent increases the viscosity of the coating liquids forming the thermosensitive coloring layer and protective layer when they are prepared and coated.
Unfortunately, due to all of these reasons, a need exists for thermosensitive recording materials having both good preservability and high degree of background whiteness.